[Nitric oxide and the upper airways: recent discoveries].

Nitric oxide (NO) is produced from L-arginine in mammalian tissues. Nitric oxide synthase (NOS) catalyzes this reaction in human tissues. It has been shown that NO serves as an important signaling molecule in the cardiovascular system and is responsible for vasoregulation. In 1991, NO was discovered in exhaled air. More recently, it has been shown that the main production site of exhaled NO is the nose and sinuses. In the upper airways NO upregulates ciliary motility and provides a first-line defense mechanism against microorganisms by antiviral and antimicrobial activity. In the lungs it is involved in ventilation/perfusion matching. Nitric oxide is also a marker for inflammation, with increased nasal output in allergic rhinitis, and a decreased output in sinusitis, nasal polyps and Kartagener's syndrome. This report reviews some aspects of the origin, metabolism, and functions of NO in the upper airways, together with the techniques for, and implications of, nasal NO measurement.